There has been quite a bit of activity in the area of instruments for detecting and measuring electric effects responsive to physiological changes that accompany emotional stresses. One category of such devices is well known under the commonly used term "lie detectors." Historically, one of the pioneer instruments was developed in the 1920s by Dr. John A. Larson. It worked on the basis of simultaneously measuring blood pressure and respiration, and coupling the responses to recording pens writing on a traveling chart. Since most instruments record more than one physiological variation, they are usually called "polygraphs".
In the device disclosed herein attention is directed to electrical resistance variations between at least two spaced points on the skin of a person or other animal or mammal. Examples of such devices can be seen in the U.S. Pat. Nos. to Eilenberger 2,379,955, Wilhelm 2,535,249, Barnett 2,933,542, and Lukacs 2,638,401.
Most of these patents show one or more forms of electric amplifiers with individual "0" or zero settable means comprising either a D.C. voltage or an A.C. voltage across the electrodes as they are applied to the surface or skin of the test subject. By measuring the amount of current that flows after application of a specific voltage across the skin-flesh-skin path using the relationship expressed by Ohm's Law (E=IR), an indication of the test subject's unknown physiologically-induced resistance changes can be obtained. Usually this is done by what is known as a push-pull circuit similar to that shown in Lukacs U.S. Pat. No. 2,638,401. These are normally in the form of what is known as a bridge circuit so that the unknown varying resistance can be compared to a known or standard resistance and be expressed in terms of this relationship.